I. Field of the Invention
This invention relates generally to respiratory gas flow measuring devices, and more particularly to a low-cost, disposable pneumotachograph flowmeter incorporating a hydrophobic fabric screen to thereby obviate the need for a built-in heater commonly found in devices of this type.
II. Discussion of the Prior Art
Medical diagnostic equipment employed to assess pulmonary performance of a subject requires an accurate measurement of respiratory gas flow during inspiration and expiration. A device often used to accomplish this end is a pneumotachograph flowmeter. It is commonly referred to as a Fleisch flowmeter and is available through the Hans Rudolph Company of St. Louis, Mo. That device comprises a tubular housing having a metal screen extending transversely to the direction of fluid flow through the tubular housing. Pressure sensing ports pass through the wall of the tubular member on opposite sides of the metal screen. The pressure differential measured across the two ports during inspiration and expiration provide an indication of the fluid flow through the screen.
In that respiratory gas is heavily ladened with water vapor, it can condense and collect on the metal screen and thereby adversely impact the accuracy of the flow measurement. To counteract this problem, the Fleisch pneumotachograph incorporates one or more screens that are arranged to be electrically heated to a temperature that precludes condensation of water vapor thereon. However, the addition of the heating elements to the device necessarily increases its cost to the point where discarding it after a single use becomes prohibitive. This is true even though the cleaning and sterilization steps following use is a necessary cost consideration.